It is relatively easy to feed pellets of plastic material into an extruder. The feed entrance down into the extruder barrel can be relatively small, because the pellets drop by gravity and are readily received into the channels between revolving flights of a rotating feed screw to become conveyed and processed downstream within the extruder barrel by the rotating feed screw.
When dealing with flowable molten plastic material being fed into an extruder, the situation is quite different from handling predictable, gravity-fed pellets. Some molten plastic materials exhibit increased stickiness with increasing temperature; others become less sticky with higher temperature. Some molten plastic materials are relatively stiff or have relatively high viscosity; others are relatively flexible or exhibit relatively low viscosity, and others have intermediate characteristics. The result of these variations in characteristics and in consistencies in flowable molten plastic materials has often caused difficulties and problems in attempting to feed such materials into rotating feed screw flights and into the barrel of an extruder. Moreover, new formulations of such materials may evidence unpredictable and inconsistent characteristics of stickiness, viscosity, etc.